Three projects: 1. How does an E. coli antimutator reduce spontaneous mutagenesis. The antimutator is a Pur B ts allele and conditionally (temperature or adenine dependent) affects base substitution mutagenesis. 2. A new genetic locus for stable RNA synthesis at 52 degrees on the E. coli map was identified by mutants. 3. The prophage (P2) inhibits T7 growth in (P2) lysogens. Mutants of both P2 and T7 have been obtained and genes identified that determine this inhibition.